1. Field of the Invention
The present invention relates to an image reading apparatus which reads an image on an original.
2. Description of the Related Art
An image reading apparatus reads an image by irradiating an original with original-reading illumination light emitted by a light source, and condensing the reflected light from the original to form an image on a photoelectric transduction unit. Therefore, in order that the image reading apparatus read the original accurately, it is necessary to bring the original into close contact with a placement stand glass plate so that the illumination light is reflected accurately.
In order to bring the original into close contact with the placement stand glass plate, it is necessary to prevent uplift of the original by bringing an original pressure plate, which presses the original, into close contact with the placement stand glass plate on which the original is placed. However, when the original pressure plate is brought into close contact with the placement stand glass plate, the original pressure plate may stick to the placement stand glass plate. In a case of an openable and closable original pressure plate, for example, when the original pressure plate is opened about a fulcrum shaft, a gripping portion, which is formed for lifting the original pressure plate, may be damaged.
To address this problem, there is disclosed an image reading apparatus in which close-contact releasing members configured to release the close contact between the original pressure plate and the placement stand glass plate are provided between the original pressure plate and the placement stand glass plate, thereby reducing the close contact between the original pressure plate and the placement stand glass plate when the original pressure plate is lifted (Japanese Patent Application Laid-Open No. 2006-67051).
However, in the image reading apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-67051, when an original having, for example, a curl, fold, or waviness is placed on the original stand glass plate and is pressed by the original pressure plate, uplift of the original occurs by an amount corresponding to a difference in height between the close-contact releasing members and the original stand glass plate. Consequently, the close contact of the original is not maintained, resulting in a distortion occurring in an image obtained through the reading. Such an image distortion tends to be more conspicuous at end portions in a main scanning direction, which have the largest field angle. In addition, as the image reading apparatus is further downsized, an optical path length becomes shorter, and the end portions are disadvantageous for the uplift of the original because of the field angle.